1. Field of the Invention
The present invention relates to an assembly jig for assembling an optical fiber gyro having an optical fiber coil which comprises a number of turns of an optical fiber having a length of several tens of meters, for example, and a method of assembling such an optical fiber gyro.
2. Description of the Related Art
There have recently been proposed and used automobile navigation systems which use a gyroscope for detecting the bearing of the automobile that incorporates such an automobile navigation system. An optical fiber gyro which is highly easy and convenient to operate, small in size and light in weight, free of mechanically movable parts, highly durable, and highly accuracy has been proposed for use as a gyroscope in automobile navigation systems. Development activities are presently in progress to put optical fiber gyros to use.
The optical fiber gyro comprises an optical fiber coil which comprises a number of turns of an optical fiber having a length of several tens of meters, and serves as a sensor for detecting an angular velocity from a phase difference (Sagnac phase difference) between two lightwaves that are propagated in opposite directions through the optical fiber coil. There are two types of optical fiber gyros, i.e., an open-loop optical fiber gyro and a closed-loop optical fiber gyro.
The open-loop optical fiber gyro is of a simple structure. However, since the open-loop optical fiber gyro employs analog detection of a light level, the scale factor thereof tends to vary if the average light level changes due to a change in a loss caused by the optical system.
The closed-loop optical fiber gyro operates by generating an optical phase bias between lightwaves passing in opposite directions for thereby canceling out a Sagnac phase difference. The closed-loop optical fiber gyro determines an angular velocity from the phase bias that has been established. Because the closed-loop optical fiber gyro directly detects a phase difference, it has better scale factor accuracy. However, the closed-loop optical fiber gyro requires an optical integrated circuit to be inserted in an optical path as a high-speed phase modulator which has sufficiently good frequency characteristics, and hence is relatively complex in structure. Nevertheless, since the closed-loop optical fiber gyro provides the level of performance that is comparable to those gyros which are used in inertial navigation systems for aircrafts, the closed-loop optical fiber gyro may possibly be a final candidate for high-performance interferrometric optical fiber gyros.
There has also been proposed an open-loop optical fiber gyro whose scale factor is electrically corrected. The proposed open-loop optical fiber gyro has sufficient performance for use in automobile navigation systems though it is not comparable to gyros in inertial navigation systems for aircrafts.
A process of assembling optical fiber gyros which are small in size, light in weight, and durable in use comprises the steps of winding an elongate optical fiber around a cylindrical object to produce a fiber coil, optically connecting an optical IC chip (optical waveguide) which incorporates a phase modulator to two ends of the optical fiber extending from the fiber coil, optically connecting an optical fiber from a light source to an optical fiber leading to a photodetector with a coupler, optically connecting an optical fiber extending from the coupler to the optical IC chip, and packaging the optical IC chip. Therefore, the assembling process is highly complex.
The fiber coil, when produced, is removed from the cylindrical object, and the ends of the optical fiber extending from the fiber coil are secured in position by a tape or the like. Therefore, during the assembling process, some of the turns of the fiber coil may become loose, and the fiber coil needs to be manually turned. The optical fiber extending from the coupler is very long, and tends to present an obstacle when it is optically connected to the optical IC chip. When the optical IC chip is packaged, it is necessary to bundle and support the elongate optical fiber so that the elongate optical fiber will not impose excessive loads on the optical IC chip. These complexities lower the efficiency of the assembling process.
Consequently, the assembling process for the conventional optical fiber gyros is time-consuming, and poses limitations on efforts to reduce the cost of the manufacture of the conventional optical fiber gyros.